The Collaborative International Dictionary of English v.0.48:

Pithy \Pith"y\, a. [Compar. Pithier; superl. Pithiest.]
   1. Consisting wholly, or in part, of pith; abounding in pith;
      as, a pithy stem; a pithy fruit.
      [1913 Webster]

   2. Having nervous energy; forceful; cogent.
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            This pithy speech prevailed, and all agreed.
                                                  --Dryden.
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            In all these Goodman Fact was very short, but pithy.
                                                  --Addison.
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   Pithy gall (Zool.), a large, rough, furrowed, oblong gall,
      formed on blackberry canes by a small gallfly
      (Diastrophus nebulosus).
      [1913 Webster]

WordNet (r) 3.0 (2006):

pithy
    adj 1: concise and full of meaning; "welcomed her pithy
           comments"; "the peculiarly sardonic and sententious style
           in which Don Luis composed his epigrams"- Hervey Allen
           [syn: pithy, sententious]

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "pithy":
   Spartan, abbreviated, abridged, allegorical, aphoristic,
   aposiopestic, associational, axiomatic, baccate, brief, brusque,
   clipped, close, compact, compendious, compressed, concise,
   condensed, connotational, connotative, contracted, crisp, curt,
   cut, definable, denotational, denotative, docked, doughy,
   edematous, effective, elliptic, epigrammatic, expressive, extended,
   extensional, figurative, flabby, fleshy, forceful, formulaic,
   formulistic, full of meaning, full of point, full of substance,
   gnomic, indicative, intelligible, intensional, interpretable,
   laconic, lean, macerated, masticated, meaning, meaningful, meaty,
   medullary, metaphorical, mushy, pasty, platitudinous, pointed,
   pregnant, proverbial, pruned, pulpal, pulpar, pulped, pulplike,
   pulpy, pungent, readable, referential, reserved, sententious,
   short, short and sweet, shortened, significant, significative,
   soft, spongy, squashy, squelchy, squishy, substantial, succinct,
   succulent, suggestive, summary, symbolic, synopsized, taciturn,
   terse, tight, to the point, transferred, truncated